Fire Agate is a mineral with a hardness of 7 out of 10 on the Mohs scale of mineral hardness [?]. These Trigonally structured gems are made of silicon dioxide, their full chemical compound being SiO2.

Fire Agate is a term applied to much of the variety of chalcedony that occurs as botryoidal, consisting of crystals of minute platy inclusion of an iron mineral goethite or limonite minerals over the layers of chalcedony, producing a vivid rainbow containing every color in the spectrum, an iridescent, fire-like appearance, with careful polishing away of the brown outside layers. When polished, it looks like opal, and is hard enough to resist fading, cracking and scratching.

This iridescence is created by the Schiller effect as found in mother-of-pearl, caused by the alternating silica and iron oxide layers which diffract and allow light to pass and form interference of colors known as fire. This effect arises from light interference within the microstructure layering of the gem, and not from any actual object inside the stone.

It is found in California and Arizona (USA), and certain parts of Northern Mexico.

Agates are found as nodules or geodes in siliceous volcanic rocks (melaphyre, porphyry) with sizes varying from a fraction of an inch to a circumference of several yards. The bands are formed by rhythmic crystallization, but scientific opinions vary as to how.

"Fire agate" is also used as a misleading term for a type of glass.

The specific gravity [?] for Fire Agate is 2.61, it's refractive index [?] is 1.53-1.54, and it's double refraction [?] is 0.004.

History

The name agate is derived from the sicilian river Achates where agates were probably found in antiquity. Its distinction as "fire agate" describes its appearance as very much like looking at fire.


Fire agates were probably formed during massive volcanic activity of the Tertiary Period, this time of volcanism when hot water, saturated with silica and iron oxide, repeatedly filled cracks and bubbles in the surrounding rock.

Industrial Usages

When cut and polished carefully as a cabochon only a very thin layer of chalcedony covers the inclusions. This material has been set in jewelry.

You May Also Like...

Agate Chalcedony

Agate Chalcedony: Agate Chalcedony differs from other Chalcedony in that it often has distinct banding. In fact some slices of Agate may appear to have banding similar to that of tree rings. Due to its porous nature it is often colored (by humans) black, red, green, or blue to further increase its visual appeal. Agate Chalcedony is found in Brazil, China, Germany ,Hungary, Mexico, Uruguay, the United States, and (read full)

Chalcedony

Chalcedony: Chalcedony is a compact form of silica, composed of microscopic quartz crystals. It is softer than quartz and denser than opal. Its appearance may range from transparent to translucent to opaque. The main types are chalcedony, which is uniformly colored, and agate, which has curved bands or zones of varying color. Varieties include the red to reddish brown, translucent carnelian, the red, opaqu (read full)

Onyx

Onyx: Onyx is a translucent to semitransparent variety of Agate, which in turn is a variety of Chalcedony or cryptocrystalline quartz that is porous and consists of straight or parallel banded agate of alternating shades of milky white and black, gray and black, black and red, white and red, white and brown. The term onyx has been erroneously applied as a suffix to Brazilian onyx, Mexican onyx, Orient (read full)

Sardonyx

Sardonyx: Sardonyx is a gem variety of reddish-brown colored sard with white or black banded chalcedony or onyx, used to make cameo with the raised black, red, or brown background. It is an example of a layer stone subvariety of Chalcedony, which in turn is a cryptocrystalline variety of Quartz.
Layer stones are multi-layered materials used in the art of gem-carving and engraving, also called glyptog (read full)

Chrysoprase

Chrysoprase: Chrysoprase is a massive, translucent, dull leek-green to yellow-green compact quartz aggregate, a variety of chalcedony. It is a crystalline quartz leek-green in color containing swarm of green hair-like fibers amphibole actinolite, which is responsible for green color. Its color is caused by fibrous ferrohornblende aggregates or disseminated chlorite minerals. The stone is more translucent than (read full)

Tags

fire agatechalcedonybotryoidalrainbowfirevividiridescentopalachatestertiary periodcabochonsilicon dioxide

Terms

Double Refraction or dr is the ability of a mineral to separate a refracted ray of light into 2 rays. If held over an image or text it will display the object 2x its original size.

Mohs Scale of Mineral Hardness is the standard used to categorize a mineral's ability to resist scratching. It gets its name from Friedrich Mohs, the German geologist who first created the scale.

RI or Refractive Index defines light's ability to move through the mineral or in a general sense, any material.

SG or Specific Gravity is the ratio of the weight of any substance to that of pure water at temperature of 3.98°C(39.2°F) and standard atmospheric pressure. This is important to note when actively seeking these minerals in the wild. Minerals with a higher SG will settle below material with a lower sg over time.